London : After 23 years of painstaking laboratory work and a program of major trials in seven countries, the 67-year-old biologist says the clinical case for the vaccine is almost proved.
It's a breakthrough moment that could save hundreds of thousands of lives, but when it comes to public health in the developing world, Cohen knows hard science is only half the job.
That's why the softly spoken U.S.-Italian researcher found himself one chilly December evening pitching his life's work to rich-world politicians whose voters will have to foot the bill, and fielding questions over festive mince pies and wine in a leather and oak-clad room in London's Houses of Parliament.
How cost-effective will the vaccine be compared to tried and tested low-tech approaches like mosquito nets and insecticides, one inquirer asks. Is there any evidence that it will bring down the spread of the disease in general, helping those who haven't been vaccinated? How long is a shot likely to stay effective?
Is there a danger it might foster a false sense of security? As the session goes on, it's clear that enthusiasm for Cohen's work is coupled with wariness among the experts and well-informed lawmakers. The bottom-line question: is the vaccine -- and the global health community's aim of completely eradicating a disease that kills a child every 45 seconds -- really worth the money?
It may seem an absurd thing to ask. Malaria threatens half the people on the planet and kills around 800,000 people a year, many of them too young to have even learned to walk.
The death rate has come down in the last decade, but full-scale eradication will cost billions and drag funds away from other equally, or possibly even more urgent health efforts.
As governments in poor countries and donors from wealthy ones weigh up where to put their money, experts have begun a quiet but fundamental debate about whether wiping out malaria is realistic or even makes economic sense.
"With all of the money and human capacity in the world, there is very little doubt that we could eliminate malaria. The question is: What is the best value for our dollar? And this is an increasingly pressing question as we look at the global economic climate," says malaria expert Oliver Sabot, who works at the Clinton Health Access Initiative in Boston.
TARGETING THE PARASITE
What is the best value for our dollar? The answer to that question seems obvious to someone like Loyce Dama Karisa, a Kenyan woman who recently gave birth to her seventh child, a girl called Rehema.
Karisa has come in a minibus full of other mothers and babies to a clinic in the mud-and-thatch village of Madamani in the Kilifi district on Kenya's south coast.
GlaxoSmithKline, the British-based drugmaker Cohen works for, is using the clinic as part of Africa's biggest ever medical experiment, giving the vaccine to babies and young children in a trial designed to assess its efficacy. "I wanted my child to get this vaccine," Karisa says. "Malaria is a very bad disease."
In the Kilifi District Hospital, the children's high- dependency unit is full of malaria patients. Listless babies and toddlers lie motionless in adult-sized beds, tangles of tubes taped to their nostrils, arms and legs.
One boy has his hands bandaged into stumps to stop him pulling a tube out of his nose. He screams and thrashes about as a drip is attached to a vein in his foot.
Mothers in mint green hospital gowns watch silently. One cradles her tiny sleeping baby's hand in her own while a ceiling fan chops slowly through the hot air, doing nothing to reduce the draining heat.
Families in Kilifi, which despite its lush green vegetation has poor soil for growing crops and high levels of poverty, are almost numb to the ravages of malaria. It's a similar story across the continent: around 90 percent of malaria's victims live in sub-Saharan Africa; most of those are under five.
The disease is caused by a parasite carried in the saliva of mosquitoes. GSK's vaccine goes to work at the point the parasite enters the human bloodstream after a mosquito bite.
By stimulating an immune response, it can prevent the parasite from maturing and multiplying in the liver. Without that response, the parasite re-enters the bloodstream and infects red blood cells, leading to fever, body aches and in some cases death.
The vaccine Cohen and his colleagues have developed combines technology from GSK's hepatitis B shot with pieces of the malaria parasite, and adds in a chemical known as an adjuvant to boost the body's immune response further.
The result - the first ever vaccine against a human parasite, as opposed to simple bacteria or viruses - is a product that could be given alongside standard infant vaccines and has been shown in a Phase II, or mid-stage, clinical trial to reduce the risk of clinical episodes of malaria in young children by 53 percent over eight months.
The pivotal Phase III program, the one baby Rehema is part of, will inject the last of 16,000 African children by February. If all goes according to plan, the vaccine could be licensed and rolled out as soon as 2015.
GSK's chief executive Andrew Witty says the trials are going well and he's looking forward to bringing the vaccine to market - something he says won't make shareholders in his company any money, but will make them proud. "This is the first vaccine that has any effect at all against a parasite-borne infection. If we went back 20 or 25 years, people would have said it was impossible," he told Reuters.
An efficacy rate of around 50 percent means the vaccine will be no panacea. Scientists and health experts normally like a success rate of at least 80 percent before a vaccine is accepted for widespread use.
There are concerns that the availability of shots could instill a false sense of protection, leading people to neglect other measures like mosquito nets.
But added to the already extensive range of nets, insecticides and anti-malarial drug treatments, the vaccine -- known as RTS,S or Mosquirix -- could prove a powerful new tool.
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